In certain fuze applications, munitions are fired by rapidly discharging to the fuze energy from a capacitor charged to a high voltage. The rapid discharge from the capacitor creates a high current flow to a fuze. A device called a spark gap is sometimes used to conduct a large amount of current when a specified voltage is applied. The spark gap must conduct current at a given threshold voltage, but must not conduct current at a lower operating voltage. Two spark gap type devices are currently in use for firing munitions, namely, a silicon controlled rectifier (SCR) and a gas discharge tube. The SCR is a solid state device having an anode, a cathode and a gate. When a suitable voltage is applied to the gate, current flows between the anode and the cathode. However, an SCR does not have the high current capability required to switch a high voltage. Therefore, it is not suitable for many applications.
The gas discharge tube has been used where higher currents are encountered. Gas discharge tubes are expensive to manufacture. They are in the form of a sealed gas filled tube having anode, cathode and trigger electrodes positioned within the tube. The tube is designed such that a high voltage applied between the anode and the cathode is insufficient to break down the gap between the anode and the cathode. However, when a lower voltage is applied to the trigger electrode, the breakdown voltage between the anode and the cathode is reduced to below the applied voltage and a rapid discharge occurs. A trigger energy of perhaps 0.5 millijoules may control, for example, the discharge of 2 millijoules or more to fire a munitions fuze, such as an exploding foil initiator bridge.
Modern munitions have a solid state electronic fuze arming and firing circuit. The overall circuit reliability is reduced and the manufacturing cost is increased when a gas discharge tube is used in conjunction with the arming and firing circuit. The gas discharge tube is both expensive to manufacture and expensive to install in the firing circuit. For a conventional gas discharge tube, as many as 6 electrical connections must be made and the tube must be physically mounted on the circuit board, for example, by the use of clamps or solder or an epoxy adhesive. Further, sufficient space must be provided for mounting the tube, which may be relative large.